1. Field of the Invention
The present invention relates to lens devices and to photographing apparatuses including television cameras, video cameras, television lenses, video lenses, or the like on which lens devices are installed.
2. Description of the Related Art
The structure of television lenses for broadcasting television cameras, such as electronic news gathering (ENG) cameras, that have recently been used for news reports, relays, dramas, variety shows, and documentaries, will be described with reference to FIGS. 17 to 19.
FIG. 17 is an external view of an ENG camera zoom lens viewed from above. FIG. 18 is an external view of the ENG camera zoom lens viewed from the side.
Referring to FIGS. 17 and 18, a lens-barrel 100 contains a fixed focus lens, a movable focus lens, a zoom lens, an iris mechanism, a relay lens, and an extender. A focus ring 101 adjusts the focus by rotating to move the movable focus lens back and forth along an optical axis. A zoom ring 102 adjusts the zoom by rotating to move the zoom lens back and forth along the optical axis. An iris ring 103 adjusts the diameter of an iris diaphragm by rotating. A drive unit 104 is installed on the lens-barrel 100 of the ENG zoom lens and includes a motor for motor-driving the zoom, focus, and iris, a position detector, a control circuit, and a clutch and a switch for selecting between motor-driving the zoom, focus, and iris and manually driving the zoom, focus, and iris. A zoom switch 105 controls motor-driving of the zoom. An iris motor/manual switch 106 is used for selecting between motor-driving the iris and manually driving the iris. A lens cable 107 is an electrical interface between the ENG lens and the ENG camera. The lens cable 107 is used for supplying a command signal to motor-drive the iris from the ENG camera and for supplying position signals of the zoom lens, the focus lens, and the iris mechanism to the ENG camera. A zoom switch speed control knob 108 is used for changing the driving speed of the zoom lens with respect to the control input to the zoom switch 105 when the zoom is motor-driven. A zoom clutch 109 is used for selecting between motor-driving the zoom and manually driving the zoom. A focus clutch 110 is used for selecting between driving the focus based on demand and manually driving the focus.
FIG. 19 shows the structure of the ENG camera and the ENG camera zoom lens.
Referring to FIG. 19, a television lens 200 includes the lens-barrel 100, the lens cable 107, and the like. A television camera 201 is connected to the lens cable 107 and includes a charge-coupled device (CCD) 40, a video signal processing unit 41, a video signal recording and playback unit 42, a video signal display unit 43, and the like.
A zoom speed command signal generation unit 1 detects a zoom speed command signal for instructing the zoom driving direction and the zoom driving speed, which are proportional to the control input to the zoom switch 105, in order to motor-drive a zoom optical system 9. The zoom speed command signal generation unit 1 includes an analog detector, such as a potentiometer or a control knob, and a digital detector, such as a rotary encoder. A zoom speed command signal operation unit 2 performs signal level conversion/signal shift conversion for taking the zoom speed command signal into an analog-to-digital (A/D) conversion unit 3. The A/D conversion unit 3 converts an analog signal output from the zoom speed command signal operation unit 2 into a digital signal. A central processing unit (CPU) 4 controls the operation of each unit of the television lens 200. A digital-to-analog (D/A) conversion unit 5 converts a zoom control signal, which is a digital signal, output from the CPU 4 to motor-drive the zoom optical system 9 into an analog signal. A zoom control signal operation unit 6 performs signal level conversion/signal shift conversion on the zoom control signal output from the D/A conversion unit 5. A zoom power amplifying unit 7 drives a zoom motor 8. The zoom motor 8 drives the zoom optical system 9. The zoom optical system 9 adjusts the power of an optical device.
A zoom absolute position signal detection unit 10 outputs a zoom absolute position signal corresponding to the absolute position of the zoom optical system 9. A zoom absolute position signal operation unit 11 performs signal level conversion/signal shift conversion for taking the zoom absolute position signal into an A/D conversion unit 12. The A/D conversion unit 12 converts an analog signal output from the zoom absolute position signal operation unit 11 into a digital signal.
A zoom switch speed control position signal operation unit 13 performs signal level conversion/signal shift conversion for taking a zoom switch speed control position signal into an A/D conversion unit 14. The A/D conversion unit 14 converts an analog signal output from the zoom switch speed control position signal operation unit 13 into a digital signal.
A zoom demand unit 15 is connected to the television lens 200. The zoom demand unit 15 controls the zoom optical system 9 using a zoom demand operation unit 16. The zoom demand operation unit 16 controls the zoom optical system 9 by adjusting the rotation angle. A zoom demand counter 17 detects a zoom driving position signal that is proportional to the angle of rotation given by the zoom demand operation unit 16. The zoom demand counter 17 includes an analog detector, such as a potentiometer or a control knob.
A D/A conversion unit 18 converts a focus control signal, which is a digital signal, output from the CPU 4 to motor-drive a focus optical system 22 into an analog signal. A focus control signal operation unit 19 performs signal level conversion/signal shift conversion on the focus control signal output from the D/A conversion unit 18. A focus power amplifying unit 20 drives a focus motor 21. The focus motor 21 drives the focus optical system 22. The focus optical system 22 adjusts the focus of the optical device.
A focus absolute position signal detection unit 23 outputs a focus absolute position signal corresponding to the absolute position of the focus optical system 22. A focus absolute position signal operation unit 24 performs signal level conversion/signal shift conversion for taking the focus absolute position signal into an A/D conversion unit 25. The A/D conversion unit 25 converts an analog signal output from the focus absolute position signal operation unit 24 into a digital signal.
A focus demand unit 26 is connected to the television lens 200. The focus demand unit 26 controls the focus optical system 22 using a focus demand operation unit 27. The focus demand operation unit 27 controls the focus optical system 22 by adjusting the rotation angle. A focus demand counter 28 detects a focus driving position signal that is proportional to the angle of rotation given by the focus demand operation unit 27. The focus demand counter 28 includes an analog detector, such as a potentiometer or a control knob.
A D/A conversion unit 29 converts an iris control signal, which is a digital signal, output from the CPU 4 to motor-drive an iris mechanism 33 into an analog signal. An iris control signal operation unit 30 performs signal level conversion/signal shift conversion on the iris control signal output from the D/A conversion unit 29. An iris power amplifying unit 31 drives an iris motor 32. The iris motor 32 drives the iris mechanism 33. The iris mechanism 33 adjusts the amount of light of the optical device.
An iris absolute position signal detection unit 34 outputs an iris absolute position signal corresponding to the absolute position of the iris mechanism 33. An iris absolute position signal operation unit 35 performs signal level conversion/signal shift conversion for taking the iris absolute position signal into an A/D conversion unit 36. The A/D conversion unit 36 converts an analog signal output from the iris absolute position signal operation unit 35 into a digital signal.
A lens information display unit 37 displays an operation state of the television lens 200. A volatile storage unit 38 stores various types of information of the television lens 200.
A CPU 39 controls the operation of each function of the television camera 201. The CCD (image pickup element) 40 converts an optical signal received via the television lens 200 into an electric signal and outputs the electric signal as a video signal. The video signal processing unit 41 processes the video signal output from the CCD 40. The video signal recording and playback unit 42 records and plays back the video signal processed by the video signal processing unit 41. The video signal display unit 43 displays an operation state of the television camera 201 and photographed pictures. A reference voltage generation unit 44 generates a reference voltage based on a power supplied from a power supply unit 46. A power switching unit 45 turns on or turns off the power of the television camera 201. The power supply unit 46 supplies the power to the television lens 200 and the television camera 201.
Operation of the zoom switch 105, the zoom clutch 109, and the zoom demand operation unit 16 when the zoom optical system 9 is operated using the ENG zoom lens and the ENG camera with the foregoing structure is described next. When the zoom clutch 109 is turned off and when the zoom switch 105 is operated, the control input to the zoom switch 105 is calculated using the zoom speed command signal generation unit 1, the zoom speed command signal operation unit 2, the A/D conversion unit 3, and the CPU 4. When the zoom demand unit 15 is operated, the control input to the zoom demand unit 15 is calculated using the zoom demand counter 17 and the CPU 4. At the same time, the absolute position of the zoom optical system 9 is calculated using the zoom absolute position signal detection unit 10, the zoom absolute position signal operation unit 11, and the A/D conversion unit 12. Based on these control inputs and the absolute position, the CPU 4 calculates a target position of the zoom optical system 9. Then, based on the target position, the D/A conversion unit 5, the zoom control signal operation unit 6, the zoom power amplifying unit 7, and the zoom motor 8 drive the zoom optical system 9.
Operation of the focus clutch 110 and the focus demand operation unit 27 when the focus optical system 22 is operated using the ENG zoom lens and the ENG camera with the foregoing structure is described next. When the focus clutch 110 is turned off and when the focus demand unit 26 is operated, the control input to the focus demand unit 26 is calculated using the focus demand counter 28 and the CPU 4. At the same time, the absolute position of the focus optical system 22 is calculated using the focus absolute position signal detection unit 23, the focus absolute position signal operation unit 24, and the A/D conversion unit 25. Based on the control input and the absolute position, the CPU 4 calculates a target position of the focus optical system 22. Then, based on the target position, the D/A conversion unit 18, the focus control signal operation unit 19, the focus power amplifying unit 20, and the focus motor 21 drive the focus optical system 22.
Operation of the iris motor/manual switch 106 when the iris mechanism 33 is operated using the ENG zoom lens and the ENG camera with the foregoing structure is described next. When the iris motor/manual switch 106 selects motor driving, the absolute position of the iris mechanism 33 is calculated using the iris absolute position signal detection unit 34, the iris absolute position signal operation unit 35, and the A/D conversion unit 36. At the same time, in accordance with a result of processing of the video signal processing unit 41, the CPU 39 calculates a target position of the iris mechanism 33. Then, based on the target position, the D/A conversion unit 29, the iris control signal operation unit 30, the iris power amplifying unit 31, and the iris motor 32 drive the iris mechanism 33.
Structures of an ENG camera zoom lens including an absolute position signal detection unit and a relative position signal detection unit are suggested in U.S. patent application No. 2001-055481 and U.S. Pat. No. 5,930,054.
In the known examples, however, since the position of a lens is detected using an absolute position detection unit, typified by a potentiometer, and an A/D conversion unit, the accuracy in detecting the position of the lens cannot be increased due to noise caused by friction of the potentiometer and the limited resolution of the A/D conversion unit. Also, since an A/D conversion unit is necessary, the size of the circuit may increase, and the cost may thus increase.
In contrast, a relative position detection unit, such as an optical incremental sensor or a magnetic incremental sensor, exhibits less noise and a higher resolution compared with an absolute position detection unit and does not require an A/D conversion unit. Thus, if a relative position detection unit is used, the foregoing problems can be solved.
However, if a relative position detection unit is used, an operation of setting the absolute position of a lens is required. As a result, a photographer cannot start photographing immediately after a power supply is turned on, and the number of operations required for the photographer is increased.
Since a relative position detection unit, such as an optical incremental sensor or a magnetic incremental sensor, exhibits less noise and a higher resolution compared with an absolute position detection unit and does not require an A/D conversion unit, if a relative position detection unit is used and motor driving is selected, the forgoing problems can be solved by automatically performing initialization after power supply is turned on. However, if manual driving is selected, initialization cannot be automatically performed after the power supply is turned on. Thus, it is difficult to install a relative position detection unit in a television lens having a manual driving unit. In addition, the power is turned on and turned off a large number of times depending on the intended use, and initialization may be automatically performed many times a day. As a result, a photographer cannot start photographing quickly, and the photographer may thus feel uncomfortable. Furthermore, pictures may move during initialization, and unnecessary battery power may be consumed for battery-operated apparatuses.